The major and arguably only abnormal feature of RBD is loss of muscle atonia (i.e., the loss of paralysis) during otherwise intact REM sleep (during which paralysis is not only normal but necessary). REM sleep is the stage of sleep in which most vivid dreaming occurs. The loss of motor inhibition leads to a wide spectrum of behavioral release during sleep. This extends from simple limb twitches to more complex integrated movement, in which sufferers appear to be unconsciously acting out their dreams. These behaviors can be violent in nature and in some cases will result in injury to either the patient or their bed partner.

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RBD is characterized by the dreamer acting out his or her dreams. These dreams often involve kicking, screaming, punching, grabbing, and even jumping out of bed. When awoken, a person can usually recall the dream they were having which will match the actions they were performing, but they will not be aware that they were moving. In a normal sleep cycle, REM sleep may be experienced at intervals of between 90 minutes and 2 hours every night, which means RBD episodes may occur up to four times a night. In a rare case, they may only happen once a week or once a month.[1] Episodes occur more towards the morning hours because that is when REM sleep is more frequent. The actions in an episode can result in injuries to oneself or one's bed partner. People can also respond to other people while sleeping and not even know it. This causes them to be aware of things while they are sleeping, which can result in sleep deprivation.[2]

Rapid eye movement behavior disorder (RBD) occurs when there is a loss of normal voluntary muscle atonia during REM sleep resulting in motor behavior in response to dream content. It can be caused by adverse reactions to certain drugs or during drug withdrawal; however, it is most often associated with the elderly and in those with neurodegenerative disorders such as Parkinson disease, and other neurodegenerative diseases for example multiple system atrophy and Lewy body dementia.[3]

Idiopathic RBD is when the individual's sleep structure seems to be normal but there is a significant increase in the density of REM sleep as well as the percentage of slow wave sleep. This category of RBD is more strongly linked to having a genetic component, as seen throughout familial gene patterns.[citation needed]

Research studies have alluded to physiological behavior of the body that accounts for what causes the symptoms of RBD. Findings have found associations with central nervous system dysfunction and abnormal cortical activity during REM sleep including low beta waves in the occipital lobe as well as increased theta waves in the frontal and occipital lobes.[citation needed]Magnetic resonance imaging (MRI) studies have suggested frontal lobe and pons dysfunctions in RBD patients because of the significantly lower blood flow in these portions of the brain as compared to non-RBD individuals.[4] Other electrophysiological findings include electromyogram (EMG) intensification in chin muscle tone most predominantly, as well as limb phasic twitching and prolonged excess activity of the extremities.

RBD may also be caused by brainstem damage of the neural circuits which normally manage the phenomenon of REM sleep.[5]

Because a number of parasomnias may be confused with RBD, it is necessary to conduct formal sleep studies such as polysomnography (PSG) performed at sleep centers that are experienced in evaluating parasomnias in order to establish a diagnosis.[6] In RBD, a single night of extensive monitoring of sleep, brain, and muscle activity will almost always reveal the lack of muscle paralysis during REM sleep, and it will also eliminate other causes of parasomnias.[7]

Recently, due to the limited access to PSG, attempts have been made to identify RBD from clinical interview as well as questionnaires.[8] Postuma et al. have validated a single-question screening tool for RBD (RBD1Q) that could be easily applied in general practice to the patient and their bed partner.[9] A positive answer to the RBDQ1, ‘Have you ever been told or suspected yourself, that you seem to act out your dreams while asleep (for example, punching, flailing your arms in the air, making running movement etc.)?’ should encourage the medical practitioner to consider the diagnosis of RBD as it offers good sensitivity (94%) and specificity (87%). Other questionnaires, such as the Rapid Eye Movement (REM) sleep Behavior Disorder Screening Questionnaire (RBDSQ)[10] or the REM Sleep Behavior Questionnaires – Hong-Kong[11] are available for more detailed characterisation.

RBD is treatable. Medications are prescribed for RBD based on symptoms. Low doses of clonazepam is most effective with a 90% success rate. How this drug works to restore REM atonia is unclear: It is thought to suppress muscle activity, rather than directly restoring atonia. Melatonin is also effective and can also be prescribed as a more natural alternative.[12] For those with Parkinson's and RBD, Levodopa is a popular choice. Pramipexole is another drug which can be an effective treatment option.[13] Recent evidence has shown melatonin and clonazepam to be comparably effective in treatment of RBD with patients who received melatonin treatment reporting fewer side effects.[12] In addition, patients with neurodegenerative diseases such as Parkinson's disease reported more favorable outcomes with melatonin treatment.[citation needed]

In addition to medication, it is wise to secure the sleeper's environment in preparation for episodes by removing potentially dangerous objects from the bedroom and either place a cushion round the bed or moving the mattress to the floor for added protection against injuries.[2][14][15]

Patients are advised to maintain a normal sleep schedule, avoid sleep deprivation, and keep track of any sleepiness they may have. Treatment includes regulating neurologic symptoms and treating any other sleep disorders that might interfere with sleep. Sleep deprivation, alcohol, certain medications, and other sleep disorders can all increase RBD and should be avoided if possible.[16]

The most comprehensive assessment so far has estimated RBD prevalence to be about 0.5% in individuals aged 15 to 100.[17] It is far more common in males: most studies report that only about a tenth of sufferers are female. This may partially be due to a referral bias, as violent activity carried out by men is more likely to result in harm and injury and is more likely to be reported than injury to male bed partners by women, or it may reflect a true difference in prevalence as a result of genetic or androgenic factors. The mean age of onset is estimated to be about 60 years.[18]

Various conditions are very similar to RBD in that sufferers exhibit excessive sleep movement and potentially violent behavior. Such disorders include sleepwalking and sleep terrors, which are associated with other stages of sleep, nocturnal seizures and obstructive sleep apnea which can induce arousals from REM sleep associated with complex behaviors. Because of the similarities between the conditions, polysomnography plays an important role in confirming RBD diagnosis.